This mode is indented for very slow and extremely weak signals at 4.375 baud

The author labled this mode as a 4-toned FSK that is why it is under FSK type of modes

FEC in JT4 uses a strong convolutional code with constraint length K=32, rate r=1/2, and a zero tail. This choice leads to an encoded message length of (72+31) x 2 = 206 information-carrying bits. Modulation is 4-tone frequency-shift keying (4-FSK) at 11025 / 2520 = 4.375 baud. Each symbol carries one information bit (the most significant bit) and one synchronizing bit. The two 32-bit polynomials used for convolutional encoding have hexadecimal values 0xf2d05351 and 0xe4613c47, and the ordering of encoded bits is scrambled by an interleaver. The pseudo-random sync vector is the following sequence (60 bits per line):